Switch machines are used to move railroad switch points. Many machines are manually operated, requiring an operator to physically force a manual throwing device to move, working against the weight of the switch points and the effects of friction and inertia. In response to the high physical toll such machines took on the operator, switch machines, such as those described in U.S. Pat. No. 4,938,438 to Farrell, U.S. Pat. No. 5,419,518 to Fiorenzo and U.S. Pat. No. 5,494,243 to Kuhn, were improved to provide a better mechanical advantage and ease the physical load on the operator.
Many switch machines also have power operating modes, such as those described in U.S. Pat. No. 5,775,647 to Wyatt, German Patent No. 3825182 to Windgassen et al., each of which disclose hydraulically-assisted switch machines. It is also known to use electrically powered switch machines, such as those disclosed in U.S. Pat. Nos. 6,427,950 and 6,568,641, both to Hoyer et al.
While hydraulic machines generally contain fewer parts than electrical machines and therefore are simpler and cheaper to construct and maintain, electrical machines were said to be an improvement over hydraulic machines because the hydraulic machines could be susceptible to failure due to leakages in the machine itself as well as all external pipes, conduits and hoses, and because hydraulic machines require an external source of hydraulic power, which is not always readily available. However, electrically powered machines also require a power source to operate the machine. In some lightly populated or underdeveloped areas, it may be difficult to ensure that a reliable power source is always available, and also difficult to constantly have someone checking the machine. Further, if for some reason a power source is unavailable, a powered switch machine is inoperable.
It is therefore preferable to provide a secondary manual operating mode, so that a switch machine may be operated even without power. U.S. Pat. No. 8,297,559 to Voegeli et al. describes a hand throw mechanism designed to be retrofitted on an in-tie electrical switch machine, to operate the machine in case of power loss. U.S. Pat. Nos. 6,164,601 and 7,267,304 to Scheer et al. disclose electrical switch machines with manual hand throw levers to be used when electrical power is not available. Other dual control machines are described in U.S. Pat. No. 5,417,392 to Wyatt, which provides a hand pump by which the hydraulic fluid within the system may be manipulated to operate the points. U.S. Pat. No. 4,213,588 to Bowles discloses a hydraulic actuator on a trailable switch machine having a pair of manual controls to move a hydraulic valve manually, thereby allowing manipulation of the fluid within the machine as needed to move the points. U.S. Pub. No. 2011/0049308 to Beaman et al. discloses a hydraulic switch machine in which the dual control comprises a hand pump for manual operation, and a hydraulic actuator for power operation. A directional selection lever may be used to move a first directional control valve to select manual operation, or to move a second directional control valve, which is electrically controlled by valve control solenoids, to select powered operation. Controls within the hydraulic manifold hydraulically isolate the hand pump during power operation. However, none of Wyatt, Bowles or Beaman addresses the issue of manually actuating the machine if hydraulic pressure is not available.
Another potential issue with such machines is the nature of the control over the operating mode. If an operator is in the process of manually throwing a switch and power is suddenly restored to the machine, the interdependence between the power and manual operating modes generally means that the manual throw lever could suddenly begin to move on its own with great force, potentially causing serious injuries to the operator.
In electrical switch machines, this issue has been typically addressed by disrupting the power circuit when the switch machine operates in manual mode. U.S. Pat. No. 5,504,405 to Hager discloses a powered system with a manual operating option, in which an electrical cutout switch is provided as a fail-safe mechanism. One drawback with this type of system is the possibility of tampering; with an electric motor, it is possible to bypass the cutout switch and allow the motor to operate even if the system appears to be in manual mode. U.S. Pat. No. 3,691,371 to Hylen describes a powered system with a manual operating option, in which an electrical cutout switch is provided in cooperation with a manual throw lever to prevent the motor from operating when the hand throw lever is not in its resting position. As a secondary fail-safe, Hylen also describes a lock plate that must be moved before the manual throw lever can be operated; movement of the lock plate disrupts the electrical circuit and shorts out the motor. However, as noted, a safety mechanism that relies solely on disrupting the electrical circuit may be bypassed.
With respect to hydraulic switch machines, similar steps can be taken, such as disconnecting the power source to the hydraulics when the switch machine is in manual operating mode, as described in U.S. Pat. No. 8,302,915 to Biagiotti. Again, this is not completely fail-safe, as a hydraulic motor could itself be shorted to provide power, even if its battery is disconnected.
It is therefore an object of this invention to provide a switch machine that overcomes some or all of the foregoing difficulties.
It is a further object of the invention to provide a switch machine that combines an independent hydraulic powered operating mode with an independent manual operating mode and a dual disconnect mechanism to positively mechanically prevent the machine from operating in one mode if the other mode is selected.
It is a further object of the invention to provide a switch machine that combines an independent hydraulic powered operating mode with an independent manual operating mode, a dual disconnect mechanism to positively mechanically prevent the machine from operating in one mode if the other mode is selected, and a second disconnect mechanism to positively electrically prevent the machine from operating if the dual disconnect mechanism is not properly engaged in the power operating mode.
These and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that the objects referred to above are statements of what motivated the invention rather than promises. Not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims.